The distributions of H atoms, displaced Si atoms, and vacancy-type defects in Si(100) produced by the implantation, at room temperature, of 1)&10' 35-, 60-, and 100-keV H+-ions/cm' were measured with use of ion and slow-positron beam techniques. Three different regions of damage were observed. The damage dist6butiog, did not correlate with the deposited energy distribution. A vacancy-type damage region surviving room-temperature annealing and the dynamic annealing during implantation is produced in the region where the energy of the primary Si recoils exceeds a threshold value of 2.0+0.5 keV, i.e. , an energy spike is needed for damage formation. In the region of the deposited energy peak, 8 is associated with damage consisting of SiH centers and vacancy complexes. At the end region of the implantation range, the distribution of displaced Si atoms is produced by H impurities in crystalline Si. Two dieerent recovery stages were observed. T' he first stage, at 500 K, is associated with the damage region containing vacancy-type defects and SiH centers with vacancy complexes; the recovery energy is 1.7 eV. The second stage, at 700 K, is attributed to the end region of the H range,~here the recovery energy associated with the recrystallization of Si after the H loss is 2.1 eV.
The electrical conductivity and field-effect mobility of undoped and NOPF6-doped Langmuir-Blodgett thin films of poly(3-hexylthiophene) have been measured as a function of temperature, electric field, and film thickness. These properties are compared with those of free-standing films. In undoped samples the conductivity is best described by variable-range hopping, whereas in the doped and dedoped states the model of charging-energy-limited tunneling between conducting islands is applicable. The data indicate metallic charge carrier densities within the conducting islands in the highly doped state. At electric fields close to the dielectric breakdown, a possible onset to Fowler-Nordheim tunneling is observed. As the samples become dedoped, the electrical properties indicate an increase in the average size of conducting islands, which are suggested to consist of polymer backbones separated by the alkyl side chains of neighboring molecules.(PHT). The measurements include the temperature, electric field, thickness, and pressure dependences of the conductivity, as well as the thickness and temperature dependences of the fieldeffect mobility.The applicabilities of the models of variable-range hopping and charging-energy-limited tunneling are tested, and the conductivity behavior is compared to that of free-standing films of PHT.
II. EXPERIMENTPoly(3-hexylthiophene) was prepared by the direct oxidation of 3-hexylthiophene monomer by FeC13 as described elsewhere.Free-standing films (thickness 30 -50 pm) were cast from chloroform solution. The molecular weight of the polymer was M"=75 700 g/mol and M"= 18 000 g/mol. Elemental analysis was performed by Schwarzkopf Microanalytical Laboratory, Inc. The results showed an Fe impurity concentration of about 7X 10' cm in the undoped polymer. Weight uptake measurements indicate dopant concentrations of about 20 mol% in the NOPF6and FeC13-doped polymers.
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